Children are at greater risk for developing environmental and neurotoxicant-induced adverse effects than adults. Neurotoxicants pose an even greater risk to the child with pre-existing neurobehavioral disorders and an already dysfunctional brain. Despite these concerns, little if any research has been carried out in high risk children with neurological disorders. Children with autistic spectrum disorder (ASD) were selected for study after discussion with communities concerned about the prevalence of children neurobehavioral disorders and environmental causes, parents groups, and health and educational professionals. ASD was selected for several reasons: autism prevalence appears to be increased in New Jersey, parents of children with autism and many scientists believe that autism's outcome may be altered by environmental chemicals and by an individuals genetic susceptibility to chemical induced toxic effects. This project, in cooperation with the Exposure Assessment and Intervention Project (EAIP) will identify children with autism and examine if their neurobehavioral disorder results in an increase in exposure to neurotoxicants. The Clinical Sciences Project will determine, in the children with autism that experience regression, if the regression is associated with an increased exposure to neurotoxicants. In addition the project will determine if neurotoxicants can alter brain regional growth pattern, and if functional polymorphic variants of genes that exacerbate or protect from chemical-induced oxidative stress are risk factors for autism, acting in the children themselves or the mother.